The present invention relates to a paper machine for manufacturing a multi-layer paper web, particularly an apparatus for manufacturing of multi-layer fiber webs comprising at least two web-forming units. Such machines are known, for instance, from
1.) German Utility Model G 91 15 632 and PA1 2.) Federal Republic of Germany 40 31 038 A1.
The machines described in each of these publications comprise at least two web-forming units, and at least one of the units has a twin-wire forming zone. The web-forming units can be of various different developments. For example, combinations of a twin-wire former and a hybrid former are possible. The web-forming unit with a twin-wire zone may comprise a former with a preliminary water drainage path followed by a twin-wire zone, as shown, for instance, in Federal Republic of Germany Application OS 31 38 133. The fiber web layers produced with a twin-wire former with a pre-drainage path, however, have enormous two-sidedness due to the one-sided removal of water. With a single-wire pre-drainage path, it is known that the initial formation of the web occurs only in a lower layer of the fiber suspension fed. Therefore, the distribution of the solids in the different layers of the fiber suspension becomes progressively more non-uniform with progressive drainage. At the same time, the upper layer, which initially remains liquid, tends strongly to form clots. Obviously, upon entrance of the pre-drained fiber suspension into the twin-wire zone, the fiber mat which has already formed in the lower layer is already compacted to such an extent that the non-uniform distribution of solids in the twin-wire zone cannot be eliminated. Furthermore, it is either impossible to break up the clots which have previously formed or to only very inadequately do it. The fiber web layer produced thus has different properties on its inner side and its outer side.